Population increases and climate change have brought the possibility of global food, feed, and fuel shortages into sharp focus in recent years. Under field conditions, plant performance, for example in terms of growth, development, biomass accumulation and seed generation, depends on a plant's tolerance and acclimation ability to numerous environmental conditions, changes and stresses. Since the beginning of agriculture and horticulture, there was a need for improving plant traits in crop cultivation. Breeding strategies foster crop properties to withstand biotic and abiotic stresses, to improve nutrient use efficiency and to alter other intrinsic crop specific yield parameters, i.e. increasing yield by applying technical advances to cope with such stresses. Plants are sessile organisms and consequently need to cope with various environmental stresses. Biotic stresses such as plant pests and pathogens on the one hand, and abiotic environmental stresses on the other hand are major limiting factors for plant growth and productivity, thereby limiting plant cultivation and geographical distribution. Plants exposed to different stresses typically have low yields of plant material, like seeds, fruit or other produces. Crop losses and crop yield losses caused by abiotic and biotic stresses represent a significant economic and political factor and contribute to food shortages, particularly in many underdeveloped countries.
Plants are exposed during their life cycle also to various cold, drought, salt, cold germination, heat, and other abiotic stresses, and viral, fungal, bacterial and other biotic stresses. For example drought stress is often manifested primarily as osmotic stress, leading to the disruption of homeostasis and ion distribution in the cell (Serrano et al., 1999; Zhu, 2001a; Wang et al., 2003). Oxidative stress, which frequently accompanies high temperature, salinity or drought stress, may cause denaturation of functional or structural proteins (Smirnoff, 1998). As a consequence these, abiotic stresses often activate similar signaling pathways (Shinozaki and Ymaguchi-Shinozaki, 2000; Knight and Knight, 2001; Zhu 2001b, 2002) and cellular responses, e.g. the production of certain stress proteins, anti-oxidants and compatible solutes (Vierling and Kimpel, 1992; Zhu et al., 1997; Cushman and Bohnert, 2000). Under freezing temperatures, plant cells can lose water as a result of ice formation that starts in the apoplast and withdraws water from the symplast (McKersie and Leshem, 1994. Stress and Stress Coping in Cultivated Plants, Kluwer Academic Publishers). Physiologically these stresses are also interconnected and may induce similar cellular damage. Additionally, plants may be under salt stress. The protection strategies are similar to those of drought resistance. Since high salt content in some soils results in less available water for cell intake, its effect is similar to those observed under drought conditions.
Drought, heat, cold and salt stress have a common theme important for plant growth and that is water availability. Plants are typically exposed during their life cycle to conditions of reduced environmental water availability. Most plants have evolved strategies to protect themselves against these conditions of low water or desiccation. However, if the severity and duration of the drought are too great, the effects on plant development, growth and yield of most crop plants are profound. Such conditions are to be expected in the future due to climatic change. According to one accepted scenario of climate change, not only the weather is more variable, but the average temperature is hotter and the average rainfall is less than in the past. Most plants are not able to keep up the adaption of their protection strategies to the climatic change. Continuous exposure to drought causes major alterations in the plant metabolism. These great changes in metabolism ultimately lead to cell death and consequently yield losses.
Therefore, there is the need for inventions that are useful to farmers to limit their losses due to biotic and abiotic stress